Battery Quote Check · a second opinion

Could your battery
save that much?

A savings promise has to fit the energy you actually buy and sell. Give it your meter readings and see how much room there is.

Files stay in your browserNo accountExact, downloadable check

Invented example

Calculating…

Conditional ceiling for the loaded period.

Use your readings See the workings

01 / THE RECORDED PERIOD

Start with the meter.

Your CSV or NEM12 file

Grid import and export energy, 5, 15, 30 or 60 minute intervals. Up to 110,000 readings.

Meter / tariff display clock

A new upload requires a clock choice. Confirm with the data supplier. Times without an offset use this clock. A daylight-saving clock needs explicit offsets and per-interval rates in CSV. NEM12 here requires a fixed clock.

Preparing the invented example…

CSV format and import limits

Required columns: start,durationMinutes,importKwh,exportKwh. Values are interval kWh, not power or cumulative readings. Keep both gross channels; do not subtract one from the other.

start,durationMinutes,importKwh,exportKwh
2025-01-01T00:00:00+10:00,30,0.2,0

Optional paired columns buyRate,feedInRate give currency per kWh for every interval and override the rate controls. Readings must be actual, contiguous and ordered. Multi-register NEM12, estimated readings and gaps are rejected.

Download a small CSV example

02 / THE BATTERY & TARIFF

Make the assumptions visible.

Usable capacity · kWh

Round-trip efficiency · %

Charge limit · kW AC

Discharge limit · kW AC

Use capacity available after any backup reserve. Loss is applied on charging; discharge is lossless. This is an optimistic capacity model. Efficiency is an assumption, not a measured guarantee.

Tariff

Import · cents/kWh

Export · cents/kWh

03 / THE PROMISE

Does the quote fit?

Quoted savings for this exact period · $

Energy-bill savings only. Match the dates shown in the result. A part-year ceiling cannot test an annual promise.

Confirm each statement before comparing. Existing solar, with no battery operating in these meter readings. These are complete, actual grid import and export channels for the relevant household circuits. The quote uses these exact dates, tariff, available capacity, power limits and efficiency assumption. Tariff rates are constant throughout each meter interval. The promise excludes grid charging, VPP payments, extra solar, changed demand, demand charges, subsidies, finance and backup value.

If a statement is unknown, leave it unticked. Ask the installer for the missing assumptions.

CERTIFIED MODEL CEILING

A ceiling, with its workings.

Preparing

…

Conditional energy-bill savings ceiling for this recorded period. Rounded upward to the cent.

One comparison policy…

Unclosed model gap…

The policy is a feasible schedule in the interval model, starting empty, with its value rounded down to the cent. The gap is the distance from that policy to the certificate, not a real-world confidence interval or a guaranteed saving.

Enter a quote to compare

Load your data, set the assumptions, then compare a savings figure for the same period.

When the comparison policy saves

This chart describes the comparison policy. Each interval is grouped by its start month on the selected clock. The ceiling is calculated across the whole period.

More storage, how much room?

Same readings, rates, efficiency and power limits. These are conditional ceilings, not forecasts of returns.

The 0 kWh row means no battery and no saving. Positive capacities use an optimistic interval model; gross import and export within one interval can make its limit above zero.

Open one day.

Day on the selected fixed clock

Charging · kWhDischarging · kWhStored energy · kWh

Read the interval values

Take the workings with you.

The report includes normalized readings, tariff, assumptions, a model schedule and the exact certificate. These downloads contain your household data. Share them deliberately.

Check a saved report here

Report JSON, checked locally

Check it independently, offline

Download the offline checker ZIP, or save the four files below.

Download these four small files into the same directory as your report: check-report.mjs, audit.mjs, certificate.mjs and rational.mjs. With Node.js 20 or later:

node check-report.mjs battery-report.json

The checker uses exact fractions and does not run the optimizer. It checks the model certificate and conditional comparison, not whether the meter readings or the quote are authentic. Read the derivation and file format.

What this can settle.

Development checks, published as source

The model, importer and report have separate tests: research/battery-quote-check/verify-engine.mjs, research/battery-quote-check/verify-importer.mjs, research/battery-quote-check/verify-report.mjs, and research/battery-quote-check/verify-bundle.mjs. The source mirror supplies each complete runnable recipe where it has been reproduced. Browser integration checks are also published as research/battery-quote-check/verify-browser.mjs; they require Playwright and a browser. See the published checks. Historical benchmark source: research/battery-quote-check/real-data/extract.py and research/battery-quote-check/real-data/benchmark.mjs.

If a promise exceeds this bound and all assumptions match, it cannot fit this model of the recorded period. A promise below the ceiling is simply not ruled out. It may still be optimistic or uneconomic.

The model gives the battery perfect knowledge of the whole period and free initial stored energy. It relaxes timing inside each interval and treats the entered efficiency as exact. Actual controls, temperature, degradation, standby consumption and wiring differ from this model. Changes in those conditions, behavior, prices, generation or efficiency can change the answer in either direction, particularly when tariffs are negative.

This first version covers an existing solar household adding storage for self-consumption. It does not price a battery, calculate payback, forecast next year, value backup or model grid-charging arbitrage and VPP participation. Daily supply charges that remain unchanged cancel out.

All meter-file parsing and calculations run in this browser. The site serves the application and its ordinary site navigation; household readings are never placed in a URL, uploaded or saved to browser storage by this tool.

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